The present invention relates generally to cardiac pacemakers, and other types of implantable medical devices, which can be programmed and/or analyzed following implantation using an external diagnostic/programmer system. More particularly, the invention relates to an implantable dual-chamber pacemaker, including software routines thereof, for automatically determining atrial capture using a PVC response to prevent pacemaker-mediated tachycardia.
Implantable cardiac pacemakers commonly store a variety of different types of diagnostic data which assist the physician in evaluating both the operation of the patient""s heart and the operation of the implanted device. Depending upon the particular pacemaker and its mode of operation, this information may include, for example, a heart rate histogram (which indicates the distribution of the patient""s heart rate over a period of time, such as one month), an event histogram (which indicates the distribution of the various sensing and stimulation events), a sensor indicated rate histogram (which indicates the distribution over time of the recommended pacing rate indicated by an implanted sensor), a variety of event counters, one or more event-triggered intracardiac electrograms, and the status of the pacemaker""s battery.
The various items of diagnostic data may be retrieved from the pacemaker for display and evaluation using a pacemaker programmer/diagnostic system (xe2x80x9cprogrammerxe2x80x9d), which uses RF telemetry to communicate with the implanted device. This is typically accomplished during routine follow-up visits of the patient to the clinic, during which time the patient is asked to hold a telemetry wand in the locality of the implanted pacemaker. To read out and view a particular item of information (e.g., a heart rate histogram), the physician employs a user interface of the programmer to designate the diagnostic item to be retrieved, and then initiates the retrieval. The programmer in-turn interrogates the pacemaker to cause the pacemaker to transmit the selected diagnostic item, and then receives and displays the selected item on the screen. The physician may also initiate various types of tests using the programmer, such as a ventricular or atrial capture test which determines the minimum pulse voltage needed to effectively stimulate the respective chamber of the heart. The physician may retrieve and adjust various programmable pacing parameters, such as sensor control parameters that are used to adjust the pacing rate according to the output of an event (or other) sensor which senses electrical activity generated within the cardiac tissue.
During the follow-up visit, it is common for the physician (or other clinician) to follow a predetermined sequence or xe2x80x9cprotocolxe2x80x9d for the evaluation of the patient. The particular protocol will often vary from physician-to-physician and/or clinic-to-clinic, and may depend upon the medical condition of the patient. By way of example, a follow-up protocol may include the steps of:
(1) retrieving, viewing and printing the atrial and ventricular rate histograms;
(2) retrieving and viewing (and optionally printing) the event histogram;
(3) conducting ventricular and atrial sense tests;
(4) conducting ventricular and atrial capture tests;
(5) contingent upon the results of steps 1-4, retrieving and viewing the R-wave and P-wave histograms (indicative of the contraction of the ventricles and the atria, respectively);
(6) retrieving, viewing and printing the sensor indicated rate histogram; and
(7) if appropriate, adjusting the sensor control parameters. During each step of the protocol, the physician typically interviews the patient and records the patient""s comments. At the end of the examination, the physician normally prepares a written report, which typically includes various printouts of the retrieved diagnostic data.
One problem with current diagnostic methods used to evaluate the follow-up patient is that the physician is typically required to scroll through large volumes of data on the programmer screen, even though only selected portions of this data are significant for diagnostic purposes. This is true, for example, in the case of atrial and ventricular capture tests, in which the physician is typically presented with a snap-shot of real-time data (typically, several seconds long), and must scroll through the data to locate the point at which capture was lost. Because much of the data viewed by the physician is insignificant, the process tends to be inefficient.
Based upon the results of the pacemaker diagnostic, the physician sometimes alters the pacemaker parameters (i.e., the stored valves that specify the therapy delivered by the pacemaker). These modifications to the pacemaker parameters are typically standard given a certain set of results. However, the steps of programming each parameter change tend to be time consuming, further adding to the overall time required to complete the follow-up examination.
Many conventional pacemaker diagnostic systems merely provide historical data to the physician and are not capable of providing for real-time analysis of pacemaker parameters. Even those systems which do provide real-time analysis of some diagnostic items do not allow the clinician to modify pacemaker parameters xe2x80x9con the flyxe2x80x9d so that the clinician can immediately observe the results of such parameter modification. This can significantly reduce the physician""s ability to actively interact with the pacemaker to achieve an unambiguous result.
The present invention addresses these and other concerns by providing an improved programmer. According to one preferred embodiment, the improved programmer can automatically step through a pacemaker test sequence and automatically identify significant events or transitions (e.g., the loss of atrial or ventricular capture, substantial heart rate changes, etc.). This aspect of the invention greatly reduces the amount of time it takes a physician to evaluate pacemaker performance, since it reduces or eliminates the need for the physician to manually scroll through the test sequence.
According to another aspect of the invention, the programmer of a preferred embodiment automatically suggests pacemaker parameter modifications based upon (i) the results of the automatic analysis and (ii) patient history trends stored within the pacemaker. In order to effect a modification in a parameter, the suggested modification is presented to the physician for confirmation. This makes parameter modification essentially a xe2x80x9cone stepxe2x80x9d process.
According to yet another aspect of the invention, the programmer evaluates the pacemaker operations in real time. The evaluation of pacemaker operation on a real-time basis allows the physician to interactively modify parameters xe2x80x9con the flyxe2x80x9d and evaluate the results immediately. This in turn allows the physician to test and program the pacemaker more rapidly, and to achieve an unambiguous result. In addition, real-time analysis and interaction with the telemetry system minimizes pauses, and prevents unwanted rhythms (e.g., retrograde conduction and PMT).
According to a preferred embodiment, the programmer retrieves information stored within the pacemaker and analyzes the retrieved data in real time. The stored information can be retrieved by means of a telemetry communication link.
The pacemaker automatically lengthens a post-ventricular atrial refractory period (PVARP). The pacemaker determines atrial capture threshold by generating atrial stimulation pulses while maintaining the ventricular stimulation pulse amplitude at a level known to ensure ventricular capture, and by detecting loss of atrial capture.
In response to loss of atrial capture, a processor automatically triggers a premature ventricular contraction (PVC) response to prevent a retrograde P-wave from initiating a pacemaker-mediated tachycardia. Also in response to loss of atrial capture, the processor sets the atrial stimulation pulse amplitude to a value above the atrial capture threshold in a subsequent cardiac cycle, and restores the PVARP to its pre-test value.